Field of the Invention
The invention relates to hydraulically driven forging machines having radially arranged working pistons in cylinders each of which is connected to a piston pump through a pipe conduit, the pumps being driven synchronously by mechanical or electrical means to synchronize the working pistons of the forging machine. It is common practice to combine the piston pumps to form a so-called crank-type driving apparatus, as shown for example in German publication DE-PS No. 23 06 566 corresponding to U.S. Pat. No. 3,916,667, having four driving pistons driven by a single crankshaft and a single driving motor. It has already been realized that oil leakage losses necessitate special measures to ensure absolute synchronism between the working pistons of the forging machine, i.e. at least for the power stroke of the pistons, by correcting the stroke position as shown in German publication DE-PS 22 07 717 and the literature cited therein, corresponding to U.S. Pat. No. 3,841,125.
The measures known according to the prior art for stroke position correction of the working cylinders of the forging machine require complex and involved apparatuses and control equipment and, if at all, give only insufficient account to the effect of unequally long pipe conduits between a crank type driving apparatus and the four working cylinders of the forging machine. That is to say, in the load condition of the forging machine, compression of the hydraulic fluid in the working cylinders, drive cylinders and pipe conduits will give rise to a stroke volume loss on the pistons of the working cylinders, which may total up to 50% of the theoretical power stroke.
With the solutions which have so far become known and which apply driving apparatuses spaced apart from the forging machine, the length of the pipe conduit is a factor as such, since a pipe conduit may accommodate the tenfold volume of the stroke volume of a working piston.